EMF, Power Output, and Terminal Voltage

1. The problem statement, all variables and given/known data
A battery supplies a steady current of 5.6 A for 21s. During this time 1410J of chemical energy is transformed into electric energy, but 560J of this electric energy is transformed into heat energy inside the battery.

3. The attempt at a solution
My attempt to find the emf was (1410J)/(21s) and to multiply that by (1.6 X 10-19), since the emf is the "amount of chemical energy transformed to electric potential energy per coulomb of charge." However, I am not sure if I am to include or minus the 560J from the 1410J.
Then to find the power output, I am assuming that you would use P=VI, where the V is the emf.
After that, I don't know how to find the terminal voltage.